EP0549342B1

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Publication number: EP0549342B1
Application number: EP19920311757
Authority: EP
Inventors: Tsutami Misawa; Akira Ogiso; Rihoko Imai; Hisato Itoh
Original assignee: Mitsui Chemicals Inc
Current assignee: Mitsui Chemicals Inc
Priority date: 1991-12-26
Filing date: 1992-12-23
Publication date: 1999-03-10
Anticipated expiration: 2012-12-23
Also published as: US5446135A; EP0549342A2; EP0549342A3; DE69228591D1; US5318856A; DE69228591T2

Description

This invention relates to novel azo dyes and coppercomplex salt dyes thereof, water-soluble azo dyescontaining the azo dyes or copper complex salt dyes,and polarizing films containing the azo dyes or coppercomplex salt dyes adsorbed and oriented as dichroicdyestuff on polymer films and having high durabilityand high polarization degree.
It is now the common practice to produce apolarizing film by stretching a film of polyvinyl alcohol(PVA) or a derivative thereof or of a polyene andthen causing iodine or a dichroic dye to be adsorbed asa polarizing element on the resulting oriented film.
Among such polarizing films, those making use ofiodine as a polarizing element are excellent in initialpolarizing performance but are weak against water orheat. They are hence accompanied by a problem indurability when employed over a long period of time under high temperature and humidity conditions. To improvetheir durability, it is contemplated, for example,to enhance their treatment in an aqueous solutioncontaining formaldehyde or boric acid or to use, as aprotective film, a polymer film having low moisturepermeability. Their durability is however still insufficientunder high temperature and moisture conditions.
Polarizing films making use of a dichroic dye asa polarizing element have better durability againstwater and heat compared with polarizing films usingiodine but are inferior in polarizing ability to thelatter. With a view toward improving this drawback,polarizing films using an organic dye as a polarizingelement and improved in heat resistance and polarizingability are proposed in Japanese Patent Laid-Open No.313568/1989 [Chem. Absts. 112(24): 218407r] and JapanesePatent Laid-Open No. 12606/1991 [Chem. Absts.115(4): 38339y]. When employed as polarizing films,such organic dyes are generally used in combinationwith a dye having absorption in a particular wavelengthrange to provide the polarizing films with a neutralcolor. It is therefore the current situation thatdepending on the dyes employed, such polarizing filmsmay undergo a substantial color change at high temperatures.
The dyes disclosed in JP-A-3-12606 are of theformula (A) or copper complexes derived therefrom:
(wherein in formula (1), A denotes a benzene ring ornaphthalene ring which may have a methyl group; R denotesan amino group, methylamino group, ethylamino group orphenylamino group, respectively). An example of such acopper complex salt is formula (B):
US-A-2,982,764 discloses dyes for cellulose materials,the dyes having the formula (C):
where A may be a benzene or naphthalene sulphonic acidgroup; Z₁ and Z₂ may be,inter alia, alkyl or alkoxy (and one may be hydrogen); Y may be,inter alia hydrogen,alkyl or alkoxy; and B represents the radical of an m-hydroxynaphthalenemonosulphonic acid bound to the azogroup in o-position to the hydroxyl group and containingan acylamino group in the β-position in the nucleushaving no sulphonic acid group.
An object of the present invention is to provide adye-base polarizing film, and a preferred embodiment maybe a high-quality polarizing film capable of exhibitingpolarizing ability comparable with iodine-base polarizingfilms and, even when two or more dyes are used incombination to provide a neutral color, having excellentpolarizing ability and heat resistance.
Another object of the present invention is toprovide a novel azo dye for such a film.
The present inventors have conducted extensiveresearch with a view toward obtaining a polarizing filmwhich uses a dye as a polarizing element and is excellentin polarizing ability and heat resistance, resulting inthe completion of the present invention.
The present invention therefore provides:
1) an azo dye represented by the following formula(1):
wherein A means a benzene or naphthalene ring havinga sulfo group or a salt thereof, Y and Z individuallydenote a group of the following formula (a):
wherein R² is a hydrogen atom, a methyl group, amethoxyl group or an ethoxyl group and R³ is a methyl,methoxyl or ethoxyl group, R¹ represents an amino, C_1-4alkylamino, or phenylamino group bonded to the 6 or 7position of the naphthalene ring, and X denotes ahydrogen, sodium, potassium or lithium atom, with theproviso that either (a) Y and Z are different or (b) bothR²s are hydrogen atoms and both R³s are methoxyl groups;
2) a copper complex salt dye represented by thefollowing formula (7):
wherein A means a benzene or naphthalene ring having asulfo group or a salt thereof, Y and Z² denote groups ofthe following formulas (a) and (b), respectively:
wherein R² is a hydrogen atom, a methyl group, a methoxylgroup or an ethoxyl group and R³ is a methyl, methoxyl orethoxyl group, with the proviso that when R² is a methylgroup, R³ is not a methoxyl group;
R¹ represents an amino, C_1-4 alkylamino, orphenylamino group bonded to the 6 or 7 position of thenaphthalene ring, and X denotes a hydrogen, sodium,potassium or lithium atom.
3) a water-soluble dye comprising the azo dye ofthe formula (1) or the copper complex salt dye of theformula (7); and
4) a polarizing film dyed with the water-solubledye.
The polarizing film dyed using the water-soluble dyeaccording to this invention has high heat resistance andhigh polarization degree and is therefore a polarizingfilm excellent in optical properties.
As the azo dyes of the present invention representedby the formula (1), those represented by the followingformulas (2) to (6) are particularly preferred:
wherein A, X, R¹, R² and R³ have the same meanings asdefined in the formula (1), and R⁴ represents an amino,methylamino, ethylamino, acetylamino, benzoylamino orphenylamino group bonded to the 6 or 7 position of thenaphthalene ring.
As the copper complex salt dyes represented bythe formula (7), those represented by the followingformulas (8) to (11) are especially preferred:
wherein A, X, R¹, R² and R³ have the same meanings asdefined in the formula (1), and R⁴ represents an amino,methylamino, ethylamino, acetylamino, benzoylamino orphenylamino group bonded to the 6 or 7 position of thenaphthalene ring.
The azo dyes of this invention represented by the formulas (1) to (6) can be prepared using a knowndiazotization process and coupling process like conventionalazo dyes.
Namely, an amino compound represented by the followingformula (12):A-NH₂wherein A has the same meaning as defined above isdiazotized, followed by the coupling with a compoundrepresented by the following formula (13)Y'-NH₂wherein Y' means a group represented by the followingformula (a') :
wherein R² and R³ have the samemeanings as defined above.
After the compound so obtained is diazotized again, thediazotized compound is coupled with a compoundrepresented by the following formula (14)::Z'-NH₂wherein Z' means a group represented by the formula(a') with the proviso that the combination of R² and R³may become the same as Y' only when R² is a hydrogenatom and R³ is a methoxyl group, whereby a disazo compound represented by the following formula (15) is produced:A-N=N-Y-N=N-Z-NH₂wherein A, Y and Z have the same meanings as definedabove. In the production processes of these intermediates,each diazotization can be carried out by such anormal process that a nitrite such as sodium nitrite ismixed to an aqueous solution or suspension of the aminein a mineral acid such as hydrochloric acid or sulfuricacid or alternatively by such a reverse process that anitrite is first added to a neutral to slightlyalkaline, aqueous solution of the amine and the resultingmixture is mixed with a mineral acid. Thediazotization temperature may suitably range from -10°Cto 40°C.
The coupling can be conducted by simply mixing anacidic aqueous solution of the amine in hydrochloricacid or acetic acid with the above-described dis-azosolution and then adjusting the pH of the resultantmixture to 3-7. The coupling temperature may suitablyrange from -10°C to 40°C.
The disazo compound so formed can then be subjectedto the next diazotization step either as is,namely, in the form of a solution or suspension orafter causing it to deposit by acidification or salting out and then collecting same by filtration.
The azo dyes represented by the formulas (1) to(6) can then be obtained by diazotizing the disazo compoundof the formula (15) and then coupling theresultant compound with a compound represented by thefollowing formula (16) :
wherein R¹ and X have the same meanings as definedabove.
The diazotization of the above dis-azo compoundmay be conducted by a normal process as in the abovediazotization process but a reverse process ispreferred where the dis-azo compound has very lowsolubility under acidic condition. The diazotizationtemperature may suitably range from 0°C to 40°C. Theresulting reaction mixture is in the form of a suspension.This suspension can be used in the next couplingstep either as is or after obtaining a presscake of thediazonium salt by filtration.
To conduct the coupling, the suspension orpresscake of the diazonium salt is added in portions toan aqueous alkaline solution of the coupling component.Here, an alkali is added as needed so that the pH of the reaction mixture is maintained at 8 to 11. Usablepreferred examples of the alkali include carbonatessuch as sodium, potassium and lithium carbonates, ammoniaand amines such as mono-, di- or triethanolamine.In addition, the hydroxide or bicarbonate of sodium,potassium or the like can also be used in combination.Further, a usual coupling promoter such as pyridine orurea can also be added. The coupling temperature maysuitably range from -10°C to 40°C.
After the completion of the coupling, sodiumchloride and/or potassium chloride is added as neededto perform salting out, whereby the target azo dyes ofthe formulas (1) to (6) are collected.
To obtain the copper complex salts of the water-solubledyes, said salts being represented by the formula(7) to (11), a conventional process can be followed.Namely, the water-soluble dyes of the formulas(1) to (5) are heated normally to 70-100°C togetherwith a copper salt such as copper sulfate, copperchloride or copper acetate in an aqueous solution. Atthis time, ammonia, or an organic amine such as monoethanolamine,diethanolamine, monopropanolamine orpyridine can be added as needed.
Specific examples of the compound of the formula(12) as the raw material include sulfanilic acid, metanilic acid, aniline-2,4-disulfonic acid, aniline-2,5-disulfonicacid, 2-naphthylamine-6-sulfonic acid,2-naphthylamine-4,8-disulfonic acid, 2-naphthylamine-3,6-disulfonicacid, 2-naphthylamine-5,7-disulfonicacid, 2-naphthylamine-6,8-disulfonic acid, and thelike.
Specific examples of the compounds represented bythe formula (13) or (14) include p-cresidine, 2,5-dimethoxyaniline,2,5-diethoxyaniline, o-toluidine, p-xylidine,o-anisidine and the like.
Specific examples of the compound represented bythe formula (16) include J acid (2-amino-5-naphthol-7-sulfonicacid), γ acid (2-amino-8-naphthol-6-sulfonicacid), N-methyl J acid, N-ethyl J acid, N-propyl Jacid, N-butyl J acid, N-methyl γ acid, N-ethyl γ acid,N-propyl γ acid, N-butyl γ acid, N-acetyl J acid, N-propionylJ acid, N-butyryl J acid, N-acetyl γ acid, N-propionylacid, N-butyryl γ acid, N-benzoyl J acid,N-benzoyl γ acid, N-phenyl J acid and N-phenyl γ acid,and the sodium, potassium and lithium salts thereof.
As the polymer film employed in the polarizingfilm of this invention, a hydrophilic polymer film ispreferred. Specific examples of its material includepolymers such as polyvinyl alcohol, polyvinyl formal,polyvinyl acetal and polyvinyl butyral; those obtained by modifying them with ethylene, propylene, acrylicacid, maleic acid, acrylamide or the like; and celluloseresins. These polymers are particularly usefulin that they have high solubility in water or ahydrophilic organic solvent, good compatibility withthe dyes of the present invention and excellent film-formingproperty and, when stretch-oriented subsequentto formation into films, facilitate orientation of thedyes of the present invention.
As a process for producing the polarizing filmof this invention by using the above-described polymerand the dye of this invention, the polymer is formedinto a film, followed by dyeing; or the dye of thepresent invention is added to a solution of the polymerto dye the polymer solution, followed by the formationof the dyed polymer solution into a film.
The above dyeing, film formation and stretchingcan be conducted generally in the following manner.
A polymer film is immersed at 20-80°C, preferably30-50°C for 1-60 minutes, preferably 3-20 minutes in adye bath containing the dye according to this inventionand, if necessary, inorganic salts such as sodiumchloride and sodium sulfate, and dyeing assistants suchas surface-active agents, the concentration of said dyebeing 0.1-5 wt.%, preferably 0.8-2.5 wt.% based on the polymer film to be dyed, so that the polymer is dyed.The polymer film so dyed is treated with boric acid asneeded, and is then dried.
As an alternative, the polymer is dissolved inwater and/or a hydrophilic organic solvent such as analcohol, glycerin or dimethylformamide, to which thedye according to the present invention is added to dyethe polymer solution. The polymer solution so dyed isformed into a film by solution casting, solution coating,extrusion or the like, whereby a dyed film is produced.
The concentration of the polymer dissolved in thesolvent varies depending on the type of the polymer butmay be 5-30 wt.%, preferably 10-20 wt.%. The concentrationof the dye according to the present inventiondissolved in the solvent also varies depending onthe type of the polymer, the type of the dye, thethickness of the resulting film, properties requiredupon employment as a polarizing film, and the like butmay generally be 0.1-5 wt.% with about 0.8-2.5 wt.%being preferred.
The unstretched film which has been obtained bydyeing or film formation as described above isstretched in a uniaxial direction by a suitable method.By this stretching, dye molecules are oriented to develop polarizing ability. Uniaxial stretching methodsinclude wet draw stretching, dry draw stretching, dryinter-roll compression stretching, etc. The stretchingcan be conducted by any of such methods. Although itis preferred to conduct this stretching at a draw ratioin a range of from 2 times to 9 times, a range of from2.5 times to 6 times is preferred when polyvinyl alcoholor a derivative thereof is used.
After the stretching and orientation, boric acidtreatment is applied in order to improve the water-proofnessand polarizing ability of the stretched film,By this boric acid treatment, both the light transmittanceand the polarity of the film are improved.Regarding conditions for the boric acid treatment, theboric acid concentration is generally 1-15 wt.%,preferably 3-10 wt.% and the treatment temperature maydesirably be in a range of 30-80°C, preferably 40-80°C.The treatment cannot bring about sufficient effectswhen the concentration of boric acid is lower than 1wt.% or the temperature is lower than 30°C. When theconcentration of boric acid is higher than 15 wt.% orthe temperature exceeds 80°C, the resulting polarizingfilm will be brittle. Boric acid concentrations andtreatment temperatures outside their respective rangesdescribed above are therefore not preferred.

The azo dyes represented by the formulas (1) to(6) and their copper complex salt dyes represented bythe formulas (7) to (11) can be used either singly orin combination. Moreover, combinations of one or moreother dyes with the dyes of the present invention makeit possible to produce polarizing films dyed in varioushues. When such other dyes are combined, any dyes canbe used as such other dyes as long as they have characteristicabsorption in a wavelength range differentfrom those of the dyes of the present invention and areprovided with a high degree of dichroism. The followingsare examples of particularly preferred dyes as expressedin terms of color index (C.I.) generic names:

C.I. Direct Yellow 12,	C.I. Direct Red 2,
C.I. Direct Yellow 44,	C.I. Direct Red 79,
C.I. Direct Yellow 28,	C.I. Direct Red 81,
C.I. Direct Yellow 142,	C.I. Direct Red 247,
C.I. Direct Violet 9,	C.I. Direct Blue 1,
C.I. Direct Violet 51,	C.I. Direct Blue 71
	C.I. Direct Blue 78,
C.I. Direct Orange 26,	C.I. Direct Blue 168,
C.I. Direct Orange 39,	C.I. Direct Blue 202,
C.I. Direct Orange 107,
C.I. Direct Brown 106,	C.I. Direct Green 85,
C.I. Direct Brown 223.

When water-soluble dyes or their copper complexsalt dyes represented by the formulas (1) to (11) areemployed as components for neutral colors which areused particularly widely, polarizing films capable ofexhibiting superb polarizing properties and preferredabsorption characteristics can be obtained. Moreover,their moisture resistance are excellent.
The polarizing films produced as described abovecan be used by applying various processing thereto.For example, they can be formed as films or sheets andcan be used as they are. Depending on application purposes,they can be laminated with a polymer such as atriacetate, acrylic or urethane polymer to form protectivelayers thereon. Further, transparent conductivefilms of indium-tin oxides or the like can beformed for actual applications on the surfaces of thepolarizing films by a vacuum depositing, sputtering orcoating process.
The present invention will hereinafter be describedby specific examples. It is to be noted thatthese examples are merely illustrative and are not intendedto limit the present invention thereto.
The term "polarization degree" as used herein is a value measured by the following method. Namely, twopolarizing films were placed in the optical path of aspectrophotometer with their stretched directions extendingin parallel with each other. Based on thelight transmittance (T//) so measured at the maximumabsorption wavelength in the visible range and thelight transmittance (T⊥) at the same wavelength asmeasured by superposing the two polarizing films withtheir stretched directions extending at a right angle,the polarization degree (V) was calculated using thefollowing formula:V =T// - T⊥T// + T⊥ x 100 (%)
Further, the durability in the present inventionis expressed by ΔE* which is to be defined below.Namely, the light transmittance of a polarizing filmwas measured. Its L*, a* and b* values were calculatedin accordance with the method prescribed in the JapaneseIndustrial Standard (JIS), Z8729 (Method for Specificationof Non-Luminous Objects by the L*,a*,b* colorsystem and the L*,u*,v* color system). ΔE* is a valueobtained in accordance with the following formula:(ΔE*)i,j =((ΔL*)i,j)2 + ((Δa*)i,j)2 + ((Δb*)i,j)2where,(ΔL*)i,j = (L*)i - (L*)*j(Δa*)i,j = (a*)i - (a*)*j(Δb*)i,j = (b*)i - (b*)*j
i: before durability test
j: after durability test
ΔE* values greater than 1 indicate a noticeablecolor change compared with the color in the initialstage and hence pose a problem from the standpoint ofstability in quality.
Incidentally, all designations of "part" or"parts" in the examples indicate part or parts byweight.

Example 1

Sodium 2,5-dimethyl-4-aminoazobenzene-4'-sulfonate(32.7 parts; 0.1 mole) was dissolved in 330parts of water, followed by the addition of 31 parts ofconcentrated hydrochloric acid and 6.9 parts of sodiumnitrite for diazotization. After a solution of 13.7parts of p-cresidine in an aqueous solution of hydrochloricacid was added to the reaction mixture, sodiumacetate was added to neutralize the resultant mixtureto pH 4 so that coupling was effected. After the completionof the reaction, the reaction mixture wasfiltered whereby a presscake containing 44.3 parts of adis-azo compound represented by the following formulawas obtained.
The presscake was dissolved in 2000 parts of warmwater with neutralizing by sodium hydroxide, followedby the addition of 31 parts of concentratedhydrochloric acid and 6.9 parts of sodium nitrite fordiazotization. After the completion of the diazotization,excess nitrite was decomposed by the addition ofsulfamic acid, and the resulting suspension of thediazonium salt was then added dropwise at about 20°C toa solution of 31.5 parts of N-phenyl J acid in a 10%aqueous solution of sodium carbonate so that couplingwas effected. Subsequent to stirring for 2 hours,sodium chloride was added in a great excess to inducesalting out. After the reaction mixture was stirredovernight, it was filtered, washed with a 3% aqueoussolution of sodium chloride and then dried, whereby 73parts of a tris-azo dye represented by the followingformula (17) were obtained.
Elemental analysis data: C H N S
Calculated (%) 55.40 3.79 11.90 7.78
Found (%) 55.20 3.71 12.05 7.85
The dye of the formula (17) was formulated into a0.3 g/ℓ dye bath. The dye bath was maintained at 42°C,in which a polyvinyl alcohol film of 75 µm in thicknesswas immersed to dye it for 2 minutes. The film sodyed, which was still in a wet state, was stretchedfivefold at 43°C in a 3% aqueous solution of boricacid. In the stretched state, the film was rinsed withwater and dried so that a polarizing film having abluish purple color was produced. The polarization degreeV of the polarizing film at its maximum absorptionwavelength λ_max was measured. As a result, the single-platetransmittance, λ_max and V were found to be 43%,575 nm and 99.0%, respectively.
A dye composition, which had been prepared byproportioning the dye of the formula (17), C.I. DirectYellow 12, C.I. Direct Orange 39, C.I. Direct Red 81and C.I. Direct Blue 202 at a ratio of 7:1:2:3:10, wasformulated into a 0.2 g/ℓ dye bath. The dye bath wasmaintained at 42°C, in which a polyvinyl alcohol filmof 75 µm in thickness was immersed to dye it for 4minutes. The film so dyed, which was still in a wetstate, was stretched 5 times at 43°C in a 3% aqueous solution of boric acid. In the stretched state, thefilm was rinsed with water and dried so that a polarizingfilm having a neutral color was produced. Thepolarization degree of the polarizing film at 40%single-plate transmittance was 98.5%.
ΔE* of the polarizing film of the neutral colorwas 0.7 after it had been left over for 500 hours in a100°C-dry constant-temperature room.

Example 2

In a similar manner to Example 1 except that 25.3parts of N-methyl J acid were used instead of 31.5parts of N-phenyl J acid, a tris-azo dye represented bythe following formula (18) was obtained.
Elemental analysis data: C H N S
Calculated (%) 52.03 3.84 12.87 8.42
Found (%) 52.00 3.71 12.62 8.33
A polyvinyl alcohol film was treated in anaqueous solution of the dye of the formula (18) in asimilar manner to Example 1, so that a polarizing filmwas produced. The film so obtained had a bluish purple color. The polarization degree V of the polarizingfilm at its maximum absorption wavelength λ_max wasmeasured. As a result, the single-plate transmittance,λ_max and V were found to be 43%, 575 nm and 97.5%,respectively.
In a similar manner to Example 1 except that thedye of the formula (18) was used instead of the dye ofthe formula (17), a polarizing film having a neutralcolor was produced. The polarization degree of thepolarizing film at 40% single-plate transmittance was98.0%.
ΔE* of the polarizing film of the neutral colorwas 0.8 after it had been left over for 500 hours in a100°C-dry constant-temperature room.

Example 3

2-Amino-4,8-naphthalenesulfonic acid (30.3 parts;0.1 mole) was dissolved in 600 parts of water, followedby the addition of 31 parts of concentrated hydrochloricacid and 6.9 parts of sodium nitrite fordiazotization. After the completion of the reaction,excess nitrite was decomposed by the addition of sulfamicacid, to which a solution of 12.2 parts of p-xylidinein an aqueous solution of hydrochloric acidwas added. Then, sodium acetate was added at 15-20°Cto neutralize the resultant mixture to pH 4 so that coupling was effected. After the completion of thereaction, precipitated crystals were collected by filtration,whereby 42.5 parts of a mono-azo compoundrepresented by the following formula was obtained.
The mono-azo compound so obtained was neutralizedwith sodium hydroxide and dissolved in 500 parts ofwater, followed by the addition of 31 parts of concentratedhydrochloric acid and 6.9 parts of sodiumnitrite for diazotization. After the completion of thediazotization, excess nitrite was decomposed by the additionof sulfamic acid. After a solution of 13.7parts of p-cresidine in an aqueous solution ofhydrochloric acid was added to the reaction mixture,sodium acetate was added at 15-20°C to neutralize theresultant mixture to pH 4 so that coupling was effected.After the completion of the reaction, theprecipitated crystals were collected by filtration,whereby 56.1 parts of a dis-azo compound represented bythe following formula were obtained.
The dis-azo compound so obtained was thereafterneutralized with sodium hydroxide and dissolved in 2000parts of warm water, followed by the addition of 31parts of concentrated hydrochloric acid and 6.9 partsof sodium nitrite for diazotization. After the completionof the diazotization, excess nitrite wasdecomposed by the addition of sulfamic acid, and theresulting suspension of the diazonium salt was thenadded dropwise at about 20°C to a solution of 31.5parts of N-phenyl J acid in a 10% aqueous solution ofsodium carbonate so that coupling was effected. Subsequentto stirring for 2 hours, sodium chloride wasadded in a great excess to induce salting out. Afterthe reaction mixture was stirred overnight, the reactionproduct was collected by filtration, washed with a3% aqueous solution of sodium chloride and then dried,whereby 77 parts of a tris-azo dye represented by thefollowing formula (19) were obtained.
Elemental analysis data: C H N S
Calculated (%) 51.69 3.30 10.05 9.86
Found (%) 51.50 3.41 10.22 9.77
A polyvinyl alcohol film was treated in anaqueous solution of the dye of the formula (19) in asimilar manner to Example 1, so that a polarizing filmwas produced. The film so obtained had a bluish purplecolor. The polarization degree V of the polarizingfilm at its maximum absorption wavelength λ_max wasmeasured. As a result, the single-plate transmittance,λ_max and V were found to be 43%, 585 nm and 99%,respectively.
In a similar manner to Example 1 except that thedye of the formula (19) was used instead of the dye ofthe formula (17), a polarizing film having a neutralcolor was produced. The polarization degree of thepolarizing film at 40% single-plate transmittance was98.5%.
ΔE* of the polarizing film of the neutral colorwas 0.7 after it had been left over for 500 hours in a100°C-dry constant-temperature room.

Examples 4-62

In a similar manner to Examples 1-3, dyes of theformula (1) shown in Table 1 were obtained. In the table, each hue, λ_max and polarization degree are thoseobserved or measured upon production of a polarizingfilm by the single use of the corresponding dye, whileeach ΔE* is a value upon production of a polarizingfilm of a neutral color by the use of the correspondingdye instead of the dye of the formula (17) in Example1.

Example 63

Ten parts of the dye of the formula (17) describedin Example 1 were dissolved in 100 parts ofwater. After 12 parts of monoethanolamine were added,an aqueous solution of 2.6 parts of crystalline coppersulfate was added, followed by heating at 90°C for 3hours. Sodium chloride was added and the resultantmixture was cooled, whereby the reaction product wassalted out. After the reaction mixture was stirredovernight, the reaction product was collected by filtration,washed with a 5% aqueous solution of sodiumchloride and then dried, so that 9 parts of a coppercomplex salt dye represented by the following formula(20) were obtained.
Elemental analysis data: C H N S
Calculated (%) 51.00 3.12 11.25 7.36
Found (%) 51.12 3.07 11.23 7.28
A polyvinyl alcohol film was treated in anaqueous solution of the dye of the formula (20) in asimilar manner to Example 1, so that a polarizing filmwas produced. The film so obtained had a bluish purple color. The polarization degree V of the polarizingfilm at its maximum absorption wavelength λ_max wasmeasured. As a result, the single-plate transmittance,λ_max and V were found to be 43%, 605 nm and 98%,respectively.
In a similar manner to Example 1 except that thedye of the formula (20) was used instead of the dye ofthe formula (17) employed in Example 1, a polarizingfilm having a neutral color was produced. Thepolarization degree of the polarizing film at 40%single-plate transmittance was 98%.
ΔE* of the polarizing film of the neutral colorwas 0.9 after it had been left over for 500 hours in a100°C-dry constant-temperature room.

Example 64

Ten parts of the tris-azo dye of the formula (19)described in Example 3 were dissolved in 100 parts ofwater, followed by the addition of 14 parts ofmonoethanolamine and then 2.8 parts of copper sulfate.The mixture so obtained was heated to conduct a complexingreaction at 90-95°C. After the completion ofthe reaction, sodium chloride was added so that thereaction product was salted out. The reaction productwas collected by filtration and then dried, whereby 9.5parts of a copper complex salt dye represented by the following formula (21) were obtained.
Elemental analysis data: C H N S
Calculated (%) 48.12 2.76 9.58 9.40
Found (%) 48.01 2.61 9.42 9.35
A polyvinyl alcohol film was treated in anaqueous solution of the dye of the formula (21) in asimilar manner to Example 1, so that a polarizing filmwas produced. The film so obtained had a bluish purplecolor. The polarization degree V of the polarizingfilm at its maximum absorption wavelength λ_max wasmeasured. As a result, the single-plate transmittance,λ_max and V were found to be 43%, 615 nm and 98%,respectively.
In a similar manner to Example 1 except that thedye of the formula (21) was used instead of the dye ofthe formula (17) employed in Example 1, a polarizingfilm having a neutral color was produced. Thepolarization degree of the polarizing film at 40%single-plate transmittance was 98%.
ΔE* of the polarizing film of the neutral colorwas 0.9 after it had been left over for 500 hours in a 100°C-dry constant-temperature room.

Examples 65-102

In a similar manner to Examples 63 and 64, thecopper complex salt dyes shown in Table 2 were prepareusing the dyes of the formula (1) as raw materials. Inthe table, each hue, λ_max and polarization degree arethose observed or measured upon production of apolarizing film by the single use of the correspondingdye, while each ΔE* is a value upon production of apolarizing film of a neutral color by the use of thecorresponding dye instead of the dye of the formula(17) in Example 1.

Comparative Example 1

In a similar manner to Example 1 except that thedye synthesized in Example 1 was replaced by the dyedisclosed in Example 1 of Japanese Patent Laid-Open No.313568/1989 and represented by the following structuralformula (A):
a polarizing film was produced. The polarization degreeof the polarizing film at its 580 nm maximum absorptionwavelength and 43% single-plate transmittancewas 96%, which was inferior to those of the polarizingfilms obtained using the dyes of the present invention.
In a similar manner to Example 1, a polarizingfilm having a neutral color was also produced. Thepolarization degree of the polarizing film at 40%single-plate transmittance was 97%.
ΔE* of the polarizing film of the neutral colorwas 2.1 after it had been left over for 500 hours in a100°C-dry constant-temperature room, which was inferiorto those of the neutral-color polarizing films obtained using the dyes of the present invention as measured inthe heat-resistance tests, respectively.

Comparative Example 2

In a similar manner to Example 1 except that thedye synthesized in Example 1 was replaced by the dyedisclosed in Example 3 of Japanese Patent Laid-Open No.12606/1991 and represented by the following structuralformula (B) :
a polarizing film was produced. The polarization degreeof the polarizing film at its 600 nm maximum absorptionwavelength and 43% single-plate transmittancewas 97%, which was inferior to those of the polarizingfilms obtained using the dyes of the present invention.
Similarly to Example 1, a polarizing film havinga neutral color was also produced. The polarizationdegree of the polarizing film at 40% single-platetransmittance was 96.5%.
ΔE* of the polarizing film of the neutral colorwas 2.5 after it had been left over for 500 hours in a 100°C-dry constant-temperature room, which was inferiorto those of the neutral-color polarizing films obtainedusing the dyes of the present invention as measured inthe heat-resistance tests, respectively.

Claims

An azo dye represented by the following formula(1):
wherein A means a benzene or naphthalene ring having asulfo group or a salt thereof, Y and Z individuallydenote a group of the following formula (a):
wherein R² is a hydrogen atom, a methylgroup, a methoxyl group or an ethoxyl groupand R³ is a methyl, methoxyl or ethoxylgroup,
R¹ represents an amino, C_1-4 alkylamino,or phenylamino group bonded tothe 6 or 7 position of the naphthalene ring, and
X denotes a hydrogen, sodium, potassium or lithiumatom, with the proviso that either (a) Y and Z are different,or (b) both R²s are hydrogen atoms and both R³s aremethoxyl groups.
An azo dye of claim 1, which is representedby the following formula (2):
wherein A, X and R¹ have the same meanings as definedin the formula (1).
An azo dye of claim 1, which is representedby the following formula (3):
wherein A, X and R¹ have the same meanings as definedin the formula (1).
An azo dye of claim 1, which is representedby the following formula (4):
wherein A, X, R² and R³ have the same meanings asdefined in the formula (1), and R⁴ represents an amino,methylamino, ethylamino, orphenylamino group bonded to the 6 or 7 position of thenaphthalene ring.
An azo dye of claim 1, which is representedby the following formula (5):
wherein A, X and R¹ have the same meanings as definedin the formula (1).
An azo dye of claim 1, which is representedby the following formula (6):
wherein A, X, R¹, R² and R³ have the same meanings asdefined in the formula (1).
A copper complex salt dye represented by thefollowing formula (7):
wherein A means a benzene or naphthalene ring having asulfo group or a salt thereof, Y and Z² denote groupsof the following formulas (a) and (b), respectively:
wherein R² is a hydrogen atom, a methylgroup, a methoxyl group or an ethoxyl groupand R³ is a methyl, methoxyl or ethoxylgroup, with the proviso that when R² is a methyl group, R³ is not a methoxyl group;
R¹ represents an amino, C_1-4 alkylamino,or phenylamino group bonded tothe 6 or 7 position of the naphthalene ring, and
X denotes a hydrogen, sodium, potassium or lithiumatom.
A copper complex salt dye of claim 7, whichis represented by the following formula (8):
wherein A, X and R¹ have the same meanings as definedin the formula (7).
A copper complex salt dye of claim 7, whichis represented by the following formula (9):
wherein A , X and R¹ have the same meanings as definedabove in the formula (7).
A copper complex salt dye of claim 7, whichis represented by the following formula (10):
wherein A, X, R² and R³ have the same meanings asdefined in the formula (7), and R⁴ represents an amino,methylamino, ethylamino, orphenylamino group bonded to the 6 or 7 position of thenaphthalene ring.
A copper complex salt dye of claim 7, whichis represented by the following formula (11):
wherein A, X and R¹ have the same meanings as definedin the formula (7).
A water-soluble dye comprising (A) an azo dyerepresented by the following formula (1):
wherein A means a benzene or naphthalene ring having asulfo group or a salt thereof, Y and Z individuallydenote a group of the following formula (a):
wherein R² is a hydrogen atom, a methyl group, a methoxylgroup or an ethoxyl group and R³ is a methyl, methoxyl orethoxyl group, R¹ represents an amino, C_1-4 alkylamino, orphenylamino group bonded to the 6 or 7 position of thenaphthalene ring, and X denotes a hydrogen, sodium,potassium or lithium atom, with the proviso that either(a) Y and Z are different or (b) both R²s are hydrogenatoms and both R³s are methoxyl groups; or (B) a coppercomplex dye obtained by complexing with copper said azodye of formula (1) with the further proviso that R³ is nota methyl group; said copper complex dye being representedby the following formula (7):
where Z² denotes a group of the following formula (b):
A water soluble dye of claim 12, wherein theazo dye is according to any of claims 2-6.
A polarizing film dyed with a water-soluble dyeaccording to claim 12 or 13.
A polarizing film of claim 14 which has beenobtained by stretching a dyed polymer film at a drawratio of from 2 times to 9 times.
A polarizing film of claim 15, wherein thepolymer film is made of at least one material selectedfrom the group consisting of polyvinyl alcohol, polyvinylformal, polyvinyl acetal and polyvinyl butyral; thoseobtained by modifying polyvinyl alcohol, polyvinylformal, polyvinyl acetal and polyvinyl butyral withethylene, propylene, acrylic acid, maleic acid oracrylamide; and cellulose resins.